Patent GB-1483545-A (GB)
Title: Transmission ratio-engagement control
IPC: F16H63/02
Filed: 1975-08-06
Abstract: 1483545 Change speed and clutch control GENERAL MOTORS CORP 6 Aug 1975 [28 Aug 1974] 32858/75 Headings F2D and F2L A device for controlling the rate of engagement of a fluid-pressure-engaged friction driveestablishing means, shown as two drive means such as clutches and brakes for establishing speed ratios in a multi-ratio transmission, driven, e.g. by a gas turbine, comprises a trimmer valve 86, 103 for each such drive means, which regulates an exhaust 91 from the drive means under control of a bias pressure 78 which increases with torque demand to result in drive-engaging pressure-increase at a constant low rate, which is the same for all torque demands, e.g. along pressure-time lines CD, KL and HJ, Fig. 2, for idle, half and full throttle, and the supply rate of the bias pressure 78 itself is so controlled that initially, for any drive engagement, e.g. from neutral to first (N-1) or for the on-going drive-establishing means during any ratio shift, the bias pressure starts at zero and increases in accordance with torque demand, so that drive engagement pressure increases from the idle point C at a rate higher than the constant low rate along a line Cnm as far as the transition point n or m corresponding to the particular torque demand, and thereafter follows the constant low rate line, e.g. to L or J. The transition points nm can be shifted towards or away from the end points HK in accordance with the rate of advance of the throttle. In all cases a final rapid increase to line pressure F follows. On selecting first ratio 17 at idle throttle from neutral (N-1) at a manual N-1-2 or automatic shift valve 23, line pressure 22, at a constant 100 p.s.i., is supplied directly to the clutch 17, and drive pressure initially rises to a point B, taking up slack, and then rapidly to an initial idle slip point C. Engaging pressure 24 now passes through a restrictor 92 in the differentially-landed spool 88 of the first ratio trimmer 86 to move the spool and a plug 94 downwards against a spring 96 to increase spool loading and hence drive pressure 24 along the constant rate idle line CD, during which, at E, a non-slip idle drive is established, whilst, at maximum idle torque D, the plug 94 is arrested by a stop 98, and engaging pressure rises rapidly to line pressure at F and then remains constant along FG. The restrictor 92, opposing spring 96, and any steady torqueresponsive bias pressure 78 in a bias chamber 97, therefore result in the same constant slope lines CD, KL, HJ, for the corresponding torquedemands. The control of the initial rate of increase of torque-responsive bias pressure 78, resulting in the initial steeper slope engaging pressure line Cnm, is as follows. Bias pressure control.-Bias pressure 78 is produced by a bias regulator valve 66 loaded in the downward, pressure-decrease direction, by modulator pressure 41 from a modulator valve 31, itself also loaded downwards in the pressure decrease direction by compressor discharge pressure 11 so that both these valves perform a pressure inversion and bias pressure 78 is directly torque responsive in a range zero to 30 p.s.i. The bias regulator valve 66 regulates line pressure 22 supplied to it through two restrictors 76, 77, so that it can supply the bias pressure system only at a controlled, limited volume, constant, slow rate. Bias pressure 78 is supplied to the lower bias chambers 97, 97<SP>1</SP> and 109 of the trimmers and an accumulator 104, increasing upward loading and causing the trimmers to regulate an increased pressure, resulting in the drive pressureincrease lines KL and HJ for medium and full throttle respectively at the same rate as that of the idle line CD, as determined by the trimmer restrictor 92. The effect of bias pressure 78 in producing the steeper pressure rise line Cnm is determined by the volumetric rate at which the bias regulator 66 can supply the bias pressure system consisting of the trimmers 86, 103 and accumulator 104, the instantaneous bias pressure being modified by the changes in volume of their pressure chambers during operation. The bias pressure supply rate is fixed at a constant value by the flow restrictors 76, 77 between supply line 22 and the bias regulator 66. In the N-1 shift the volume of the second ratio trimmer chamber 97<SP>1</SP> remains unchanged at its maximum, shown. and the liquid expelled by the first ratio trimmer 86 as the volume of its chamber 97 is reduced by descent of the plug 94 during a trim cycle, is accepted by increasing the volume 109 of the accumulator 104 and by the bias regulator 66. The increase in bias pressure necessary to produce an initial pressure increase with torque demand, from the idle point C to points K or H on the constant rate lines KL, HJ corresponding to the particular torque demand, is thereby delayed and engagement pressure increase occurs along the line Cnm in accordance with the rate at which bias pressure can itself increase as determined by the volume change of the bias system and the volumetric rate of supply thereto from the bias regulator valve 66. The rate of change of torque demand also influences the rate of change of bias pressure, rapid throttle advance shifting the points nm nearer to KH. Transient shift pressure control.-During a shift, e.g. 1-2, the N-1-2 control valve 23 exhausts the first ratio clutch 17 and its pressure drops rapidly, XY, Fig. 2, under control of the trimmer restrictor 92 as the plug 94 moves the first ratio trimmer valve spool to its uppermost, re-set, position shown. The increase in volume of the trimmer chamber 97 is compensated by liquid expelled by the accumulator 104, and the timing provided by the trimmer restrictor 92 and bias pressure rate of flow restrictors 66, 67 is such that bias pressure 87 is zeroized just before the trimmer 86 and accumulator 104 reach their initial positions shown, and just before the plug 94<SP>1</SP> of the second ratio trimmer 103 begins its descent, point C, Fig. 2, controlling engagement of second ratio drive pressure according to the respective lines shown in Fig. 2, as described above for N-1 shift.